dt-bindings/gic-v3: Add msm8996 compatible string

Access to GICR_WAKER is restricted on msm8996 SoC in Hypervisor.
There are many devices out there with this restriction in place
and there has been no update to this firmware since last few years,
making those devices totally unusable for upstream development.

IIDR register value conflicts with other SoCs, using compatible seems
to be the only way to apply quirks required for msm8996 based SoCs.

Without this quirk many qcom SoCs (atleast 3 that I know) are
unable to boot mainline.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>